1. Field of the Invention
This invention relates to thermocouples and more particularly to a thermocouple which by reason of erosion substantially continuously provides a conducting path between the thermocouple wires.
2. Background of the Prior Art
The use of thermocouple wires to provide a continuous e.m.f. as a signal corresponding to the temperature of a heated surface in a furnace lining is well known.
It has been common practice to enclose the thermocouple within a protective metal tube as shown in the U.S. patents to Haselton, et al., U.S. Pat. No. 3,416,972, Scanlon, et al., U.S. Pat. No. 3,505,124, Inouye, U.S. Pat. No. 3,580,744, and Bingham, U.S. Pat. No. 3,317,453. Such metal tubes by reason of their heat conductivity along the thermocouple adversely affect the operation by reducing the temperature gradient along the thermocouple and introduce undesired chemical reactions at the exposed end.
It has also been proposed, as shown in the U.S. patents to Haselton, et al., U.S. Pat. No. 3,416,972, Black, et al., U.S. Pat. No. 3,463,674, and Bingham, No. 3,317,383 to surround one or both of the wires with compacted mineral oxide insulation. None of these thermocouples are intended to act nor are they capable of substantially continuously providing a conducting path between the wires.
Strimple, et al., in U.S. Pat. No. 3,845,706, show a thermocouple having a pair of dissimilar wires twisted on each other or parallel, at least one of the wires being insulated with glass insulating material such as a fiberglass sleeve. The wires are contained within an outer sleeve made of metallic or non-metallic material such as stainless steel or fiberglass of sufficient strength and rigidity to contain between the outer sleeve and the wires powdered refractory material consisting of chrome ore, chromium oxide or admixtures thereof, packed into the outer sleeve, for forming a conducting path upon heating of the glass insulating sleeve to relatively high temperatures in the presence of the chrome ore or chromium oxide.
The Strimple structure is difficult to maintain as to size and requires more space, is limited as to the selection of refractory material and this in turn does not permit of change of range and in its operation had more discontinuities in its action.